IngressRoute: add an option to disable cross-namespace routing

Co-authored-by: Jean-Baptiste Doumenjou <925513+jbdoumenjou@users.noreply.github.com>

docs/content/providers/kubernetes-crd.md

@@ -250,6 +250,34 @@ providers:
 --providers.kubernetescrd.throttleDuration=10s
 ```
 
+### `allowCrossNamespace`
+
+_Optional, Default: true_
+
+```toml tab="File (TOML)"
+[providers.kubernetesCRD]
+  allowCrossNamespace = false
+  # ...
+```
+
+```yaml tab="File (YAML)"
+providers:
+  kubernetesCRD:
+    allowCrossNamespace: false
+    # ...
+```
+
+```bash tab="CLI"
+--providers.kubernetescrd.allowCrossNamespace=false
+```
+
+If the parameter is set to `false`, an IngressRoute will not be able to reference any resources
+in another namespace than the IngressRoute namespace.
+
+!!! warning "Deprecation"
+    
+    Please notice that the default value for this option will be set to `false` in a future version.
+
 ## Further
 
 Also see the [full example](../user-guides/crd-acme/index.md) with Let's Encrypt.

docs/content/reference/static-configuration/cli-ref.md

@@ -540,6 +540,9 @@ TLS key
 `--providers.kubernetescrd`:  
 Enable Kubernetes backend with default settings. (Default: ```false```)
 
+`--providers.kubernetescrd.allowcrossnamespace`:  
+Allow cross namespace resource reference. (Default: ```true```)
+
 `--providers.kubernetescrd.certauthfilepath`:  
 Kubernetes certificate authority file path (not needed for in-cluster client).
 

docs/content/reference/static-configuration/env-ref.md

@@ -540,6 +540,9 @@ TLS key
 `TRAEFIK_PROVIDERS_KUBERNETESCRD`:  
 Enable Kubernetes backend with default settings. (Default: ```false```)
 
+`TRAEFIK_PROVIDERS_KUBERNETESCRD_ALLOWCROSSNAMESPACE`:  
+Allow cross namespace resource reference. (Default: ```true```)
+
 `TRAEFIK_PROVIDERS_KUBERNETESCRD_CERTAUTHFILEPATH`:  
 Kubernetes certificate authority file path (not needed for in-cluster client).
 

docs/content/reference/static-configuration/file.toml

@@ -113,6 +113,7 @@
     certAuthFilePath = "foobar"
     disablePassHostHeaders = true
     namespaces = ["foobar", "foobar"]
+    allowCrossNamespace = true
     labelSelector = "foobar"
     ingressClass = "foobar"
     throttleDuration = 42

docs/content/reference/static-configuration/file.yaml

@@ -123,6 +123,7 @@ providers:
     namespaces:
     - foobar
     - foobar
+    allowCrossNamespace: true
     labelSelector: foobar
     ingressClass: foobar
     throttleDuration: 42s

integration/fixtures/k8s/07-ingressroute-cross-namespace.yml

@@ -0,0 +1,120 @@
+---
+apiVersion: v1
+kind: Namespace
+metadata:
+  name: other-ns
+
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: whoami
+  namespace: other-ns
+
+spec:
+  ports:
+    - name: http
+      port: 80
+  selector:
+    app: traefiklabs
+    task: whoami
+
+---
+apiVersion: traefik.containo.us/v1alpha1
+kind: IngressRoute
+metadata:
+  name: test6.route
+  namespace: other-ns
+
+spec:
+  entryPoints:
+    - web
+  routes:
+  - match: Host(`foo.com`) && PathPrefix(`/a`)
+    kind: Rule
+    services:
+    - name: whoami
+      namespace: default
+      port: 80
+  - match: Host(`foo.com`) && PathPrefix(`/b`)
+    kind: Rule
+    services:
+    - name: wrr2
+      namespace: default
+      kind: TraefikService
+  - match: Host(`foo.com`) && PathPrefix(`/c`)
+    kind: Rule
+    services:
+    - name: wrr3
+      kind: TraefikService
+  - match: Host(`foo.com`) && PathPrefix(`/d`)
+    kind: Rule
+    services:
+    - name: whoami
+      namespace: other-ns
+      port: 80
+    middlewares:
+    - name: stripprefix2
+      namespace: default
+  - match: Host(`foo.com`) && PathPrefix(`/e`)
+    kind: Rule
+    services:
+    - name: whoami
+      port: 80
+    middlewares:
+    - name: test-errorpage
+
+---
+apiVersion: traefik.containo.us/v1alpha1
+kind: TraefikService
+metadata:
+  name: wrr2
+  namespace: default
+
+spec:
+  weighted:
+    services:
+      - name: whoami
+        port: 80
+
+---
+apiVersion: traefik.containo.us/v1alpha1
+kind: TraefikService
+metadata:
+  name: wrr3
+  namespace: other-ns
+
+spec:
+  weighted:
+    services:
+      - name: whoami
+        namespace: default
+        port: 80
+
+---
+apiVersion: traefik.containo.us/v1alpha1
+kind: Middleware
+metadata:
+  name: stripprefix2
+  namespace: default
+
+spec:
+  stripPrefix:
+    prefixes:
+      - /tobestripped
+
+---
+apiVersion: traefik.containo.us/v1alpha1
+kind: Middleware
+metadata:
+  name: test-errorpage
+
+spec:
+  errors:
+    status:
+      - 500-599
+    query: /{status}.html
+    service:
+      name: whoami
+      namespace: other-ns
+      port: 80

integration/fixtures/k8s_crd.toml

@@ -16,3 +16,4 @@
     address = ":8000"
 
 [providers.kubernetesCRD]
+  allowCrossNamespace = false

integration/k8s_test.go

@@ -53,6 +53,7 @@ func (s *K8sSuite) TearDownSuite(c *check.C) {
 		"./fixtures/k8s/coredns.yaml",
 		"./fixtures/k8s/rolebindings.yaml",
 		"./fixtures/k8s/traefik.yaml",
+		"./fixtures/k8s/ccm.yaml",
 	}
 
 	for _, filename := range generatedFiles {

integration/testdata/rawdata-crd.json

@@ -50,6 +50,20 @@
 			"using": [
 				"web"
 			]
+		},
+		"other-ns-test6-route-482e4988e134701d8cc8@kubernetescrd": {
+			"entryPoints": [
+				"web"
+			],
+			"service": "other-ns-wrr3",
+			"rule": "Host(`foo.com`) \u0026\u0026 PathPrefix(`/c`)",
+			"error": [
+				"the service \"other-ns-wrr3@kubernetescrd\" does not exist"
+			],
+			"status": "disabled",
+			"using": [
+				"web"
+			]
 		}
 	},
 	"middlewares": {
@@ -64,6 +78,14 @@
 				"default-test2-route-23c7f4c450289ee29016@kubernetescrd"
 			]
 		},
+		"default-stripprefix2@kubernetescrd": {
+			"stripPrefix": {
+				"prefixes": [
+					"/tobestripped"
+				]
+			},
+			"status": "enabled"
+		},
 		"default-stripprefix@kubernetescrd": {
 			"stripPrefix": {
 				"prefixes": [
@@ -172,6 +194,17 @@
 				"default-test3-route-7d0ac22d3d8db4b82618@kubernetescrd"
 			]
 		},
+		"default-wrr2@kubernetescrd": {
+			"weighted": {
+				"services": [
+					{
+						"name": "default-whoami-80",
+						"weight": 1
+					}
+				]
+			},
+			"status": "enabled"
+		},
 		"noop@internal": {
 			"status": "enabled"
 		}

pkg/provider/kubernetes/crd/fixtures/services.yml

@@ -199,3 +199,33 @@ spec:
     - name: http
       protocol: TCP
       port: 8080
+
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: whoami-svc
+  namespace: cross-ns
+
+spec:
+  ports:
+    - name: web
+      port: 80
+  selector:
+    app: traefiklabs
+    task: whoami
+
+---
+kind: Endpoints
+apiVersion: v1
+metadata:
+  name: whoami-svc
+  namespace: cross-ns
+
+subsets:
+  - addresses:
+      - ip: 10.10.0.1
+      - ip: 10.10.0.2
+    ports:
+      - name: web
+        port: 80

pkg/provider/kubernetes/crd/fixtures/tcp/services.yml

@@ -208,3 +208,33 @@ metadata:
 spec:
   externalName: "fe80::200:5aee:feaa:20a2"
   type: ExternalName
+
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: whoamitcp-cross-ns
+  namespace: cross-ns
+
+spec:
+  ports:
+    - name: myapp
+      port: 8000
+  selector:
+    app: traefiklabs
+    task: whoamitcp
+
+---
+kind: Endpoints
+apiVersion: v1
+metadata:
+  name: whoamitcp-cross-ns
+  namespace: cross-ns
+
+subsets:
+  - addresses:
+      - ip: 10.10.0.1
+      - ip: 10.10.0.2
+    ports:
+      - name: myapp
+        port: 8000

pkg/provider/kubernetes/crd/fixtures/tcp/with_cross_namespace.yml

@@ -0,0 +1,16 @@
+apiVersion: traefik.containo.us/v1alpha1
+kind: IngressRouteTCP
+metadata:
+  name: test.route
+  namespace: default
+
+spec:
+  entryPoints:
+    - foo
+
+  routes:
+  - match: HostSNI(`foo.com`)
+    services:
+    - name: whoamitcp-cross-ns
+      namespace: cross-ns
+      port: 8000

pkg/provider/kubernetes/crd/fixtures/udp/services.yml

@@ -130,3 +130,33 @@ subsets:
     ports:
       - name: myapp-ipv6
         port: 8080
+
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: whoamiudp-cross-ns
+  namespace: cross-ns
+
+spec:
+  ports:
+    - name: myapp
+      port: 8000
+  selector:
+    app: traefiklabs
+    task: whoamiudp
+
+---
+kind: Endpoints
+apiVersion: v1
+metadata:
+  name: whoamiudp-cross-ns
+  namespace: cross-ns
+
+subsets:
+  - addresses:
+      - ip: 10.10.0.1
+      - ip: 10.10.0.2
+    ports:
+      - name: myapp
+        port: 8000

pkg/provider/kubernetes/crd/fixtures/udp/with_cross_namespace.yml

@@ -0,0 +1,15 @@
+apiVersion: traefik.containo.us/v1alpha1
+kind: IngressRouteUDP
+metadata:
+  name: test.route
+  namespace: default
+
+spec:
+  entryPoints:
+    - foo
+
+  routes:
+  - services:
+    - name: whoamiudp-cross-ns
+      namespace: cross-ns
+      port: 8000

pkg/provider/kubernetes/crd/fixtures/with_cross_namespace.yml

@@ -0,0 +1,91 @@
+apiVersion: traefik.containo.us/v1alpha1
+kind: IngressRoute
+metadata:
+  name: cross-ns-route
+  namespace: default
+
+spec:
+  entryPoints:
+    - foo
+
+  routes:
+  - match: Host(`foo.com`) && PathPrefix(`/bar`)
+    kind: Rule
+    priority: 12
+    services:
+    - name: whoami-svc
+      namespace: cross-ns
+      port: 80
+    - name: tr-svc-wrr1
+      kind: TraefikService
+    - name: tr-svc-wrr2
+      namespace: cross-ns
+      kind: TraefikService
+    - name: tr-svc-mirror1
+      kind: TraefikService
+    - name: tr-svc-mirror2
+      namespace: cross-ns
+      kind: TraefikService
+
+---
+apiVersion: traefik.containo.us/v1alpha1
+kind: TraefikService
+metadata:
+  name: tr-svc-wrr1
+  namespace: default
+
+spec:
+  weighted:
+    services:
+      - name: whoami-svc
+        namespace: cross-ns
+        weight: 1
+        port: 80
+
+---
+apiVersion: traefik.containo.us/v1alpha1
+kind: TraefikService
+metadata:
+  name: tr-svc-wrr2
+  namespace: cross-ns
+
+spec:
+  weighted:
+    services:
+      - name: whoami-svc
+        weight: 1
+        port: 80
+
+---
+apiVersion: traefik.containo.us/v1alpha1
+kind: TraefikService
+metadata:
+  name: tr-svc-mirror1
+  namespace: default
+
+spec:
+  mirroring:
+    name: whoami
+    port: 80
+    mirrors:
+      - name: whoami-svc
+        namespace: cross-ns
+        percent: 20
+        port: 80
+
+---
+apiVersion: traefik.containo.us/v1alpha1
+kind: TraefikService
+metadata:
+  name: tr-svc-mirror2
+  namespace: cross-ns
+
+spec:
+  mirroring:
+    name: whoami-svc
+    port: 80
+    mirrors:
+      - name: whoami-svc
+        namespace: cross-ns
+        percent: 20
+        port: 80

pkg/provider/kubernetes/crd/fixtures/with_middleware_cross_namespace.yml

@@ -0,0 +1,58 @@
+apiVersion: traefik.containo.us/v1alpha1
+kind: IngressRoute
+metadata:
+  name: test-crossnamespace.route
+  namespace: default
+
+spec:
+  entryPoints:
+    - foo
+
+  routes:
+  - match: Host(`foo.com`) && PathPrefix(`/bar`)
+    kind: Rule
+    priority: 12
+    services:
+    - name: whoami
+      namespace: default
+      port: 80
+    middlewares:
+    - name: stripprefix
+      namespace: cross-ns
+  - match: Host(`foo.com`) && PathPrefix(`/bir`)
+    kind: Rule
+    priority: 12
+    services:
+    - name: whoami
+      namespace: default
+      port: 80
+    middlewares:
+    - name: test-errorpage
+
+---
+apiVersion: traefik.containo.us/v1alpha1
+kind: Middleware
+metadata:
+  name: stripprefix
+  namespace: cross-ns
+
+spec:
+  stripPrefix:
+    prefixes:
+      - /stripit
+
+---
+apiVersion: traefik.containo.us/v1alpha1
+kind: Middleware
+metadata:
+  name: test-errorpage
+  namespace: default
+spec:
+  errors:
+    status:
+      - 500-599
+    query: /{status}.html
+    service:
+      name: whoami-svc
+      namespace: cross-ns
+      port: 80

pkg/provider/kubernetes/crd/kubernetes.go

@@ -43,6 +43,7 @@ type Provider struct {
 	CertAuthFilePath       string          `description:"Kubernetes certificate authority file path (not needed for in-cluster client)." json:"certAuthFilePath,omitempty" toml:"certAuthFilePath,omitempty" yaml:"certAuthFilePath,omitempty"`
 	DisablePassHostHeaders bool            `description:"Kubernetes disable PassHost Headers." json:"disablePassHostHeaders,omitempty" toml:"disablePassHostHeaders,omitempty" yaml:"disablePassHostHeaders,omitempty" export:"true"`
 	Namespaces             []string        `description:"Kubernetes namespaces." json:"namespaces,omitempty" toml:"namespaces,omitempty" yaml:"namespaces,omitempty" export:"true"`
+	AllowCrossNamespace    *bool           `description:"Allow cross namespace resource reference." json:"allowCrossNamespace,omitempty" toml:"allowCrossNamespace,omitempty" yaml:"allowCrossNamespace,omitempty" export:"true"`
 	LabelSelector          string          `description:"Kubernetes label selector to use." json:"labelSelector,omitempty" toml:"labelSelector,omitempty" yaml:"labelSelector,omitempty" export:"true"`
 	IngressClass           string          `description:"Value of kubernetes.io/ingress.class annotation to watch for." json:"ingressClass,omitempty" toml:"ingressClass,omitempty" yaml:"ingressClass,omitempty" export:"true"`
 	ThrottleDuration       ptypes.Duration `description:"Ingress refresh throttle duration" json:"throttleDuration,omitempty" toml:"throttleDuration,omitempty" yaml:"throttleDuration,omitempty" export:"true"`
@@ -82,6 +83,11 @@ func (p *Provider) newK8sClient(ctx context.Context) (*clientWrapper, error) {
 	return client, nil
 }
 
+// SetDefaults sets the default values.
+func (p *Provider) SetDefaults() {
+	p.AllowCrossNamespace = func(b bool) *bool { return &b }(true)
+}
+
 // Init the provider.
 func (p *Provider) Init() error {
 	return nil
@@ -98,6 +104,10 @@ func (p *Provider) Provide(configurationChan chan<- dynamic.Message, pool *safe.
 		return err
 	}
 
+	if p.AllowCrossNamespace == nil || *p.AllowCrossNamespace {
+		logger.Warn("Cross-namespace reference between IngressRoutes and resources is enabled, please ensure that this is expected (see AllowCrossNamespace option)")
+	}
+
 	pool.GoCtx(func(ctxPool context.Context) {
 		operation := func() error {
 			eventsChan, err := k8sClient.WatchAll(p.Namespaces, ctxPool.Done())
@@ -197,7 +207,7 @@ func (p *Provider) loadConfigurationFromCRD(ctx context.Context, client Client)
 			continue
 		}
 
-		errorPage, errorPageService, err := createErrorPageMiddleware(client, middleware.Namespace, middleware.Spec.Errors)
+		errorPage, errorPageService, err := p.createErrorPageMiddleware(client, middleware.Namespace, middleware.Spec.Errors)
 		if err != nil {
 			log.FromContext(ctxMid).Errorf("Error while reading error page middleware: %v", err)
 			continue
@@ -236,7 +246,7 @@ func (p *Provider) loadConfigurationFromCRD(ctx context.Context, client Client)
 		}
 	}
 
-	cb := configBuilder{client}
+	cb := configBuilder{client, p.AllowCrossNamespace}
 	for _, service := range client.GetTraefikServices() {
 		err := cb.buildTraefikService(ctx, service, conf.HTTP.Services)
 		if err != nil {
@@ -281,7 +291,7 @@ func getServicePort(svc *corev1.Service, port int32) (*corev1.ServicePort, error
 	return &corev1.ServicePort{Port: port}, nil
 }
 
-func createErrorPageMiddleware(client Client, namespace string, errorPage *v1alpha1.ErrorPage) (*dynamic.ErrorPage, *dynamic.Service, error) {
+func (p *Provider) createErrorPageMiddleware(client Client, namespace string, errorPage *v1alpha1.ErrorPage) (*dynamic.ErrorPage, *dynamic.Service, error) {
 	if errorPage == nil {
 		return nil, nil, nil
 	}
@@ -291,7 +301,7 @@ func createErrorPageMiddleware(client Client, namespace string, errorPage *v1alp
 		Query:  errorPage.Query,
 	}
 
-	balancerServerHTTP, err := configBuilder{client}.buildServersLB(namespace, errorPage.Service.LoadBalancerSpec)
+	balancerServerHTTP, err := configBuilder{client, p.AllowCrossNamespace}.buildServersLB(namespace, errorPage.Service.LoadBalancerSpec)
 	if err != nil {
 		return nil, nil, err
 	}
@@ -749,3 +759,8 @@ func throttleEvents(ctx context.Context, throttleDuration time.Duration, pool *s
 
 	return eventsChanBuffered
 }
+
+func isNamespaceAllowed(allowCrossNamespace *bool, parentNamespace, namespace string) bool {
+	// If allowCrossNamespace option is not defined the default behavior is to allow cross namespace references.
+	return allowCrossNamespace == nil || *allowCrossNamespace || parentNamespace == namespace
+}

pkg/provider/kubernetes/crd/kubernetes_http.go

@@ -48,7 +48,8 @@ func (p *Provider) loadIngressRouteConfiguration(ctx context.Context, client Cli
 			ingressName = ingressRoute.GenerateName
 		}
 
-		cb := configBuilder{client}
+		cb := configBuilder{client, p.AllowCrossNamespace}
+
 		for _, route := range ingressRoute.Spec.Routes {
 			if route.Kind != "Rule" {
 				logger.Errorf("Unsupported match kind: %s. Only \"Rule\" is supported for now.", route.Kind)
@@ -66,23 +67,10 @@ func (p *Provider) loadIngressRouteConfiguration(ctx context.Context, client Cli
 				continue
 			}
 
-			var mds []string
-			for _, mi := range route.Middlewares {
-				if strings.Contains(mi.Name, providerNamespaceSeparator) {
-					if len(mi.Namespace) > 0 {
-						logger.
-							WithField(log.MiddlewareName, mi.Name).
-							Warnf("namespace %q is ignored in cross-provider context", mi.Namespace)
-					}
-					mds = append(mds, mi.Name)
-					continue
-				}
-
-				ns := mi.Namespace
-				if len(ns) == 0 {
-					ns = ingressRoute.Namespace
-				}
-				mds = append(mds, makeID(ns, mi.Name))
+			mds, err := p.makeMiddlewareKeys(ctx, ingressRoute.Namespace, route.Middlewares)
+			if err != nil {
+				logger.Errorf("Failed to create middleware keys: %v", err)
+				continue
 			}
 
 			normalized := provider.Normalize(makeID(ingressRoute.Namespace, serviceKey))
@@ -153,8 +141,38 @@ func (p *Provider) loadIngressRouteConfiguration(ctx context.Context, client Cli
 	return conf
 }
 
+func (p *Provider) makeMiddlewareKeys(ctx context.Context, ingRouteNamespace string, middlewares []v1alpha1.MiddlewareRef) ([]string, error) {
+	var mds []string
+
+	for _, mi := range middlewares {
+		if strings.Contains(mi.Name, providerNamespaceSeparator) {
+			if len(mi.Namespace) > 0 {
+				log.FromContext(ctx).
+					WithField(log.MiddlewareName, mi.Name).
+					Warnf("namespace %q is ignored in cross-provider context", mi.Namespace)
+			}
+			mds = append(mds, mi.Name)
+			continue
+		}
+
+		ns := ingRouteNamespace
+		if len(mi.Namespace) > 0 {
+			if !isNamespaceAllowed(p.AllowCrossNamespace, ingRouteNamespace, mi.Namespace) {
+				return nil, fmt.Errorf("middleware %s/%s is not in the IngressRoute namespace %s", mi.Namespace, mi.Name, ingRouteNamespace)
+			}
+
+			ns = mi.Namespace
+		}
+
+		mds = append(mds, makeID(ns, mi.Name))
+	}
+
+	return mds, nil
+}
+
 type configBuilder struct {
-	client Client
+	client              Client
+	allowCrossNamespace *bool
 }
 
 // buildTraefikService creates the configuration for the traefik service defined in tService,
@@ -270,7 +288,7 @@ func (c configBuilder) buildServersLB(namespace string, svc v1alpha1.LoadBalance
 	return &dynamic.Service{LoadBalancer: lb}, nil
 }
 
-func (c configBuilder) loadServers(fallbackNamespace string, svc v1alpha1.LoadBalancerSpec) ([]dynamic.Server, error) {
+func (c configBuilder) loadServers(parentNamespace string, svc v1alpha1.LoadBalancerSpec) ([]dynamic.Server, error) {
 	strategy := svc.Strategy
 	if strategy == "" {
 		strategy = roundRobinStrategy
@@ -279,7 +297,11 @@ func (c configBuilder) loadServers(fallbackNamespace string, svc v1alpha1.LoadBa
 		return nil, fmt.Errorf("load balancing strategy %s is not supported", strategy)
 	}
 
-	namespace := namespaceOrFallback(svc, fallbackNamespace)
+	namespace := namespaceOrFallback(svc, parentNamespace)
+
+	if !isNamespaceAllowed(c.allowCrossNamespace, parentNamespace, namespace) {
+		return nil, fmt.Errorf("load balancer service %s/%s is not in the parent resource namespace %s", svc.Namespace, svc.Name, parentNamespace)
+	}
 
 	// If the service uses explicitly the provider suffix
 	sanitizedName := strings.TrimSuffix(svc.Name, providerNamespaceSeparator+providerName)
@@ -355,10 +377,14 @@ func (c configBuilder) loadServers(fallbackNamespace string, svc v1alpha1.LoadBa
 // In addition, if the service is a Kubernetes one,
 // it generates and returns the configuration part for such a service,
 // so that the caller can add it to the global config map.
-func (c configBuilder) nameAndService(ctx context.Context, namespaceService string, service v1alpha1.LoadBalancerSpec) (string, *dynamic.Service, error) {
+func (c configBuilder) nameAndService(ctx context.Context, parentNamespace string, service v1alpha1.LoadBalancerSpec) (string, *dynamic.Service, error) {
 	svcCtx := log.With(ctx, log.Str(log.ServiceName, service.Name))
 
-	namespace := namespaceOrFallback(service, namespaceService)
+	namespace := namespaceOrFallback(service, parentNamespace)
+
+	if !isNamespaceAllowed(c.allowCrossNamespace, parentNamespace, namespace) {
+		return "", nil, fmt.Errorf("service %s/%s not in the parent resource namespace %s", service.Namespace, service.Name, parentNamespace)
+	}
 
 	switch {
 	case service.Kind == "" || service.Kind == "Service":

pkg/provider/kubernetes/crd/kubernetes_tcp.go

@@ -55,7 +55,7 @@ func (p *Provider) loadIngressRouteTCPConfiguration(ctx context.Context, client
 			serviceName := makeID(ingressRouteTCP.Namespace, key)
 
 			for _, service := range route.Services {
-				balancerServerTCP, err := createLoadBalancerServerTCP(client, ingressRouteTCP.Namespace, service)
+				balancerServerTCP, err := p.createLoadBalancerServerTCP(client, ingressRouteTCP.Namespace, service)
 				if err != nil {
 					logger.
 						WithField("serviceName", service.Name).
@@ -125,9 +125,13 @@ func (p *Provider) loadIngressRouteTCPConfiguration(ctx context.Context, client
 	return conf
 }
 
-func createLoadBalancerServerTCP(client Client, namespace string, service v1alpha1.ServiceTCP) (*dynamic.TCPService, error) {
-	ns := namespace
+func (p *Provider) createLoadBalancerServerTCP(client Client, parentNamespace string, service v1alpha1.ServiceTCP) (*dynamic.TCPService, error) {
+	ns := parentNamespace
 	if len(service.Namespace) > 0 {
+		if !isNamespaceAllowed(p.AllowCrossNamespace, parentNamespace, service.Namespace) {
+			return nil, fmt.Errorf("tcp service %s/%s is not in the parent resource namespace %s", service.Namespace, service.Name, parentNamespace)
+		}
+
 		ns = service.Namespace
 	}
 

pkg/provider/kubernetes/crd/kubernetes_test.go

@@ -2,13 +2,21 @@ package crd
 
 import (
 	"context"
+	"io/ioutil"
+	"path/filepath"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 	"github.com/traefik/traefik/v2/pkg/config/dynamic"
 	"github.com/traefik/traefik/v2/pkg/provider"
+	crdfake "github.com/traefik/traefik/v2/pkg/provider/kubernetes/crd/generated/clientset/versioned/fake"
+	"github.com/traefik/traefik/v2/pkg/provider/kubernetes/crd/traefik/v1alpha1"
+	"github.com/traefik/traefik/v2/pkg/provider/kubernetes/k8s"
 	"github.com/traefik/traefik/v2/pkg/tls"
 	corev1 "k8s.io/api/core/v1"
+	"k8s.io/apimachinery/pkg/runtime"
+	kubefake "k8s.io/client-go/kubernetes/fake"
 )
 
 var _ provider.Provider = (*Provider)(nil)
@@ -1122,7 +1130,10 @@ func TestLoadIngressRouteTCPs(t *testing.T) {
 			}
 
 			p := Provider{IngressClass: test.ingressClass}
-			conf := p.loadConfigurationFromCRD(context.Background(), newClientMock(test.paths...))
+			p.SetDefaults()
+
+			clientMock := newClientMock(test.paths...)
+			conf := p.loadConfigurationFromCRD(context.Background(), clientMock)
 			assert.Equal(t, test.expected, conf)
 		})
 	}
@@ -3187,7 +3198,10 @@ func TestLoadIngressRoutes(t *testing.T) {
 			}
 
 			p := Provider{IngressClass: test.ingressClass}
-			conf := p.loadConfigurationFromCRD(context.Background(), newClientMock(test.paths...))
+			p.SetDefaults()
+
+			clientMock := newClientMock(test.paths...)
+			conf := p.loadConfigurationFromCRD(context.Background(), clientMock)
 			assert.Equal(t, test.expected, conf)
 		})
 	}
@@ -3495,7 +3509,10 @@ func TestLoadIngressRouteUDPs(t *testing.T) {
 			}
 
 			p := Provider{IngressClass: test.ingressClass}
-			conf := p.loadConfigurationFromCRD(context.Background(), newClientMock(test.paths...))
+			p.SetDefaults()
+
+			clientMock := newClientMock(test.paths...)
+			conf := p.loadConfigurationFromCRD(context.Background(), clientMock)
 			assert.Equal(t, test.expected, conf)
 		})
 	}
@@ -3714,3 +3731,563 @@ func TestGetServicePort(t *testing.T) {
 		})
 	}
 }
+
+func TestCrossNamespace(t *testing.T) {
+	testCases := []struct {
+		desc                string
+		allowCrossNamespace bool
+		ingressClass        string
+		paths               []string
+		expected            *dynamic.Configuration
+	}{
+		{
+			desc: "Empty",
+			expected: &dynamic.Configuration{
+				UDP: &dynamic.UDPConfiguration{
+					Routers:  map[string]*dynamic.UDPRouter{},
+					Services: map[string]*dynamic.UDPService{},
+				},
+				TCP: &dynamic.TCPConfiguration{
+					Routers:  map[string]*dynamic.TCPRouter{},
+					Services: map[string]*dynamic.TCPService{},
+				},
+				HTTP: &dynamic.HTTPConfiguration{
+					Routers:     map[string]*dynamic.Router{},
+					Middlewares: map[string]*dynamic.Middleware{},
+					Services:    map[string]*dynamic.Service{},
+				},
+				TLS: &dynamic.TLSConfiguration{},
+			},
+		},
+		{
+			desc:  "HTTP middleware cross namespace disallowed",
+			paths: []string{"services.yml", "with_middleware_cross_namespace.yml"},
+			expected: &dynamic.Configuration{
+				UDP: &dynamic.UDPConfiguration{
+					Routers:  map[string]*dynamic.UDPRouter{},
+					Services: map[string]*dynamic.UDPService{},
+				},
+				TCP: &dynamic.TCPConfiguration{
+					Routers:  map[string]*dynamic.TCPRouter{},
+					Services: map[string]*dynamic.TCPService{},
+				},
+				HTTP: &dynamic.HTTPConfiguration{
+					Routers: map[string]*dynamic.Router{
+						"default-test-crossnamespace-route-9313b71dbe6a649d5049": {
+							EntryPoints: []string{"foo"},
+							Service:     "default-test-crossnamespace-route-9313b71dbe6a649d5049",
+							Rule:        "Host(`foo.com`) && PathPrefix(`/bir`)",
+							Priority:    12,
+							Middlewares: []string{"default-test-errorpage"},
+						},
+					},
+					Middlewares: map[string]*dynamic.Middleware{
+						"cross-ns-stripprefix": {
+							StripPrefix: &dynamic.StripPrefix{
+								Prefixes:   []string{"/stripit"},
+								ForceSlash: false,
+							},
+						},
+					},
+					Services: map[string]*dynamic.Service{
+						"default-test-crossnamespace-route-9313b71dbe6a649d5049": {
+							LoadBalancer: &dynamic.ServersLoadBalancer{
+								Servers: []dynamic.Server{
+									{
+										URL: "http://10.10.0.1:80",
+									},
+									{
+										URL: "http://10.10.0.2:80",
+									},
+								},
+								PassHostHeader: Bool(true),
+							},
+						},
+					},
+				},
+				TLS: &dynamic.TLSConfiguration{},
+			},
+		},
+		{
+			desc:                "HTTP middleware cross namespace allowed",
+			paths:               []string{"services.yml", "with_middleware_cross_namespace.yml"},
+			allowCrossNamespace: true,
+			expected: &dynamic.Configuration{
+				UDP: &dynamic.UDPConfiguration{
+					Routers:  map[string]*dynamic.UDPRouter{},
+					Services: map[string]*dynamic.UDPService{},
+				},
+				TCP: &dynamic.TCPConfiguration{
+					Routers:  map[string]*dynamic.TCPRouter{},
+					Services: map[string]*dynamic.TCPService{},
+				},
+				HTTP: &dynamic.HTTPConfiguration{
+					Routers: map[string]*dynamic.Router{
+						"default-test-crossnamespace-route-6b204d94623b3df4370c": {
+							EntryPoints: []string{"foo"},
+							Service:     "default-test-crossnamespace-route-6b204d94623b3df4370c",
+							Rule:        "Host(`foo.com`) && PathPrefix(`/bar`)",
+							Priority:    12,
+							Middlewares: []string{
+								"cross-ns-stripprefix",
+							},
+						},
+						"default-test-crossnamespace-route-9313b71dbe6a649d5049": {
+							EntryPoints: []string{"foo"},
+							Service:     "default-test-crossnamespace-route-9313b71dbe6a649d5049",
+							Rule:        "Host(`foo.com`) && PathPrefix(`/bir`)",
+							Priority:    12,
+							Middlewares: []string{"default-test-errorpage"},
+						},
+					},
+					Middlewares: map[string]*dynamic.Middleware{
+						"cross-ns-stripprefix": {
+							StripPrefix: &dynamic.StripPrefix{
+								Prefixes:   []string{"/stripit"},
+								ForceSlash: false,
+							},
+						},
+						"default-test-errorpage": {
+							Errors: &dynamic.ErrorPage{
+								Status:  []string{"500-599"},
+								Service: "default-test-errorpage-errorpage-service",
+								Query:   "/{status}.html",
+							},
+						},
+					},
+					Services: map[string]*dynamic.Service{
+						"default-test-crossnamespace-route-6b204d94623b3df4370c": {
+							LoadBalancer: &dynamic.ServersLoadBalancer{
+								Servers: []dynamic.Server{
+									{
+										URL: "http://10.10.0.1:80",
+									},
+									{
+										URL: "http://10.10.0.2:80",
+									},
+								},
+								PassHostHeader: Bool(true),
+							},
+						},
+						"default-test-crossnamespace-route-9313b71dbe6a649d5049": {
+							LoadBalancer: &dynamic.ServersLoadBalancer{
+								Servers: []dynamic.Server{
+									{
+										URL: "http://10.10.0.1:80",
+									},
+									{
+										URL: "http://10.10.0.2:80",
+									},
+								},
+								PassHostHeader: Bool(true),
+							},
+						},
+						"default-test-errorpage-errorpage-service": {
+							LoadBalancer: &dynamic.ServersLoadBalancer{
+								Servers: []dynamic.Server{
+									{
+										URL: "http://10.10.0.1:80",
+									},
+									{
+										URL: "http://10.10.0.2:80",
+									},
+								},
+								PassHostHeader: Bool(true),
+							},
+						},
+					},
+				},
+				TLS: &dynamic.TLSConfiguration{},
+			},
+		},
+		{
+			desc:                "HTTP cross namespace allowed",
+			paths:               []string{"services.yml", "with_cross_namespace.yml"},
+			allowCrossNamespace: true,
+			expected: &dynamic.Configuration{
+				UDP: &dynamic.UDPConfiguration{
+					Routers:  map[string]*dynamic.UDPRouter{},
+					Services: map[string]*dynamic.UDPService{},
+				},
+				TCP: &dynamic.TCPConfiguration{
+					Routers:  map[string]*dynamic.TCPRouter{},
+					Services: map[string]*dynamic.TCPService{},
+				},
+				HTTP: &dynamic.HTTPConfiguration{
+					Routers: map[string]*dynamic.Router{
+						"default-cross-ns-route-6b204d94623b3df4370c": {
+							EntryPoints: []string{"foo"},
+							Service:     "default-cross-ns-route-6b204d94623b3df4370c",
+							Rule:        "Host(`foo.com`) && PathPrefix(`/bar`)",
+							Priority:    12,
+						},
+					},
+					Middlewares: map[string]*dynamic.Middleware{},
+					Services: map[string]*dynamic.Service{
+						"default-cross-ns-route-6b204d94623b3df4370c": {
+							Weighted: &dynamic.WeightedRoundRobin{
+								Services: []dynamic.WRRService{
+									{
+										Name:   "cross-ns-whoami-svc-80",
+										Weight: func(i int) *int { return &i }(1),
+									},
+									{
+										Name:   "default-tr-svc-wrr1",
+										Weight: func(i int) *int { return &i }(1),
+									},
+									{
+										Name:   "cross-ns-tr-svc-wrr2",
+										Weight: func(i int) *int { return &i }(1),
+									},
+									{
+										Name:   "default-tr-svc-mirror1",
+										Weight: func(i int) *int { return &i }(1),
+									},
+									{
+										Name:   "cross-ns-tr-svc-mirror2",
+										Weight: func(i int) *int { return &i }(1),
+									},
+								},
+							},
+						},
+						"cross-ns-whoami-svc-80": {
+							LoadBalancer: &dynamic.ServersLoadBalancer{
+								Servers: []dynamic.Server{
+									{
+										URL: "http://10.10.0.1:80",
+									},
+									{
+										URL: "http://10.10.0.2:80",
+									},
+								},
+								PassHostHeader: Bool(true),
+							},
+						},
+						"default-tr-svc-wrr1": {
+							Weighted: &dynamic.WeightedRoundRobin{
+								Services: []dynamic.WRRService{
+									{
+										Name:   "cross-ns-whoami-svc-80",
+										Weight: func(i int) *int { return &i }(1),
+									},
+								},
+							},
+						},
+						"cross-ns-tr-svc-wrr2": {
+							Weighted: &dynamic.WeightedRoundRobin{
+								Services: []dynamic.WRRService{
+									{
+										Name:   "cross-ns-whoami-svc-80",
+										Weight: func(i int) *int { return &i }(1),
+									},
+								},
+							},
+						},
+						"default-tr-svc-mirror1": {
+							Mirroring: &dynamic.Mirroring{
+								Service: "default-whoami-80",
+								Mirrors: []dynamic.MirrorService{
+									{
+										Name:    "cross-ns-whoami-svc-80",
+										Percent: 20,
+									},
+								},
+							},
+						},
+						"cross-ns-tr-svc-mirror2": {
+							Mirroring: &dynamic.Mirroring{
+								Service: "cross-ns-whoami-svc-80",
+								Mirrors: []dynamic.MirrorService{
+									{
+										Name:    "cross-ns-whoami-svc-80",
+										Percent: 20,
+									},
+								},
+							},
+						},
+						"default-whoami-80": {
+							LoadBalancer: &dynamic.ServersLoadBalancer{
+								Servers: []dynamic.Server{
+									{
+										URL: "http://10.10.0.1:80",
+									},
+									{
+										URL: "http://10.10.0.2:80",
+									},
+								},
+								PassHostHeader: Bool(true),
+							},
+						},
+					},
+				},
+				TLS: &dynamic.TLSConfiguration{},
+			},
+		},
+		{
+			desc:  "HTTP cross namespace disallowed",
+			paths: []string{"services.yml", "with_cross_namespace.yml"},
+			expected: &dynamic.Configuration{
+				UDP: &dynamic.UDPConfiguration{
+					Routers:  map[string]*dynamic.UDPRouter{},
+					Services: map[string]*dynamic.UDPService{},
+				},
+				TCP: &dynamic.TCPConfiguration{
+					Routers:  map[string]*dynamic.TCPRouter{},
+					Services: map[string]*dynamic.TCPService{},
+				},
+				HTTP: &dynamic.HTTPConfiguration{
+					Routers:     map[string]*dynamic.Router{},
+					Middlewares: map[string]*dynamic.Middleware{},
+					Services: map[string]*dynamic.Service{
+						"cross-ns-tr-svc-wrr2": {
+							Weighted: &dynamic.WeightedRoundRobin{
+								Services: []dynamic.WRRService{
+									{
+										Name:   "cross-ns-whoami-svc-80",
+										Weight: func(i int) *int { return &i }(1),
+									},
+								},
+							},
+						},
+						"cross-ns-whoami-svc-80": {
+							LoadBalancer: &dynamic.ServersLoadBalancer{
+								Servers: []dynamic.Server{
+									{
+										URL: "http://10.10.0.1:80",
+									},
+									{
+										URL: "http://10.10.0.2:80",
+									},
+								},
+								PassHostHeader: Bool(true),
+							},
+						},
+						"cross-ns-tr-svc-mirror2": {
+							Mirroring: &dynamic.Mirroring{
+								Service: "cross-ns-whoami-svc-80",
+								Mirrors: []dynamic.MirrorService{
+									{
+										Name:    "cross-ns-whoami-svc-80",
+										Percent: 20,
+									},
+								},
+							},
+						},
+						"default-whoami-80": {
+							LoadBalancer: &dynamic.ServersLoadBalancer{
+								Servers: []dynamic.Server{
+									{
+										URL: "http://10.10.0.1:80",
+									},
+									{
+										URL: "http://10.10.0.2:80",
+									},
+								},
+								PassHostHeader: Bool(true),
+							},
+						},
+					},
+				},
+				TLS: &dynamic.TLSConfiguration{},
+			},
+		},
+		{
+			desc:                "TCP cross namespace allowed",
+			paths:               []string{"tcp/services.yml", "tcp/with_cross_namespace.yml"},
+			allowCrossNamespace: true,
+			expected: &dynamic.Configuration{
+				UDP: &dynamic.UDPConfiguration{
+					Routers:  map[string]*dynamic.UDPRouter{},
+					Services: map[string]*dynamic.UDPService{},
+				},
+				HTTP: &dynamic.HTTPConfiguration{
+					Routers:     map[string]*dynamic.Router{},
+					Middlewares: map[string]*dynamic.Middleware{},
+					Services:    map[string]*dynamic.Service{},
+				},
+				TCP: &dynamic.TCPConfiguration{
+					Routers: map[string]*dynamic.TCPRouter{
+						"default-test.route-fdd3e9338e47a45efefc": {
+							EntryPoints: []string{"foo"},
+							Service:     "default-test.route-fdd3e9338e47a45efefc",
+							Rule:        "HostSNI(`foo.com`)",
+						},
+					},
+					Services: map[string]*dynamic.TCPService{
+						"default-test.route-fdd3e9338e47a45efefc": {
+							LoadBalancer: &dynamic.TCPServersLoadBalancer{
+								Servers: []dynamic.TCPServer{
+									{
+										Address: "10.10.0.1:8000",
+										Port:    "",
+									},
+									{
+										Address: "10.10.0.2:8000",
+										Port:    "",
+									},
+								},
+							},
+						},
+					},
+				},
+				TLS: &dynamic.TLSConfiguration{},
+			},
+		},
+		{
+			desc:  "TCP cross namespace disallowed",
+			paths: []string{"tcp/services.yml", "tcp/with_cross_namespace.yml"},
+			expected: &dynamic.Configuration{
+				UDP: &dynamic.UDPConfiguration{
+					Routers:  map[string]*dynamic.UDPRouter{},
+					Services: map[string]*dynamic.UDPService{},
+				},
+				TCP: &dynamic.TCPConfiguration{
+					// The router that references the invalid service will be discarded.
+					Routers: map[string]*dynamic.TCPRouter{
+						"default-test.route-fdd3e9338e47a45efefc": {
+							EntryPoints: []string{"foo"},
+							Service:     "default-test.route-fdd3e9338e47a45efefc",
+							Rule:        "HostSNI(`foo.com`)",
+						},
+					},
+					Services: map[string]*dynamic.TCPService{},
+				},
+				HTTP: &dynamic.HTTPConfiguration{
+					Routers:     map[string]*dynamic.Router{},
+					Middlewares: map[string]*dynamic.Middleware{},
+					Services:    map[string]*dynamic.Service{},
+				},
+				TLS: &dynamic.TLSConfiguration{},
+			},
+		},
+		{
+			desc:                "UDP cross namespace allowed",
+			paths:               []string{"udp/services.yml", "udp/with_cross_namespace.yml"},
+			allowCrossNamespace: true,
+			expected: &dynamic.Configuration{
+				UDP: &dynamic.UDPConfiguration{
+					Routers: map[string]*dynamic.UDPRouter{
+						"default-test.route-0": {
+							EntryPoints: []string{"foo"},
+							Service:     "default-test.route-0",
+						},
+					},
+					Services: map[string]*dynamic.UDPService{
+						"default-test.route-0": {
+							LoadBalancer: &dynamic.UDPServersLoadBalancer{
+								Servers: []dynamic.UDPServer{
+									{
+										Address: "10.10.0.1:8000",
+										Port:    "",
+									},
+									{
+										Address: "10.10.0.2:8000",
+										Port:    "",
+									},
+								},
+							},
+						},
+					},
+				},
+				HTTP: &dynamic.HTTPConfiguration{
+					Routers:     map[string]*dynamic.Router{},
+					Middlewares: map[string]*dynamic.Middleware{},
+					Services:    map[string]*dynamic.Service{},
+				},
+				TCP: &dynamic.TCPConfiguration{
+					Routers:  map[string]*dynamic.TCPRouter{},
+					Services: map[string]*dynamic.TCPService{},
+				},
+				TLS: &dynamic.TLSConfiguration{},
+			},
+		},
+		{
+			desc:  "UDP cross namespace disallowed",
+			paths: []string{"udp/services.yml", "udp/with_cross_namespace.yml"},
+			expected: &dynamic.Configuration{
+				// The router that references the invalid service will be discarded.
+				UDP: &dynamic.UDPConfiguration{
+					Routers: map[string]*dynamic.UDPRouter{
+						"default-test.route-0": {
+							EntryPoints: []string{"foo"},
+							Service:     "default-test.route-0",
+						},
+					},
+					Services: map[string]*dynamic.UDPService{},
+				},
+				TCP: &dynamic.TCPConfiguration{
+					Routers:  map[string]*dynamic.TCPRouter{},
+					Services: map[string]*dynamic.TCPService{},
+				},
+				HTTP: &dynamic.HTTPConfiguration{
+					Routers:     map[string]*dynamic.Router{},
+					Middlewares: map[string]*dynamic.Middleware{},
+					Services:    map[string]*dynamic.Service{},
+				},
+				TLS: &dynamic.TLSConfiguration{},
+			},
+		},
+	}
+
+	for _, test := range testCases {
+		test := test
+
+		t.Run(test.desc, func(t *testing.T) {
+			t.Parallel()
+
+			var k8sObjects []runtime.Object
+			var crdObjects []runtime.Object
+			for _, path := range test.paths {
+				yamlContent, err := ioutil.ReadFile(filepath.FromSlash("./fixtures/" + path))
+				if err != nil {
+					panic(err)
+				}
+
+				objects := k8s.MustParseYaml(yamlContent)
+				for _, obj := range objects {
+					switch o := obj.(type) {
+					case *corev1.Service, *corev1.Endpoints, *corev1.Secret:
+						k8sObjects = append(k8sObjects, o)
+					case *v1alpha1.IngressRoute:
+						crdObjects = append(crdObjects, o)
+					case *v1alpha1.IngressRouteTCP:
+						crdObjects = append(crdObjects, o)
+					case *v1alpha1.IngressRouteUDP:
+						crdObjects = append(crdObjects, o)
+					case *v1alpha1.Middleware:
+						crdObjects = append(crdObjects, o)
+					case *v1alpha1.TraefikService:
+						crdObjects = append(crdObjects, o)
+					case *v1alpha1.TLSOption:
+						crdObjects = append(crdObjects, o)
+					case *v1alpha1.TLSStore:
+						crdObjects = append(crdObjects, o)
+					default:
+					}
+				}
+			}
+
+			kubeClient := kubefake.NewSimpleClientset(k8sObjects...)
+			crdClient := crdfake.NewSimpleClientset(crdObjects...)
+
+			client := newClientImpl(kubeClient, crdClient)
+
+			stopCh := make(chan struct{})
+
+			eventCh, err := client.WatchAll([]string{"default", "cross-ns"}, stopCh)
+			require.NoError(t, err)
+
+			if k8sObjects != nil || crdObjects != nil {
+				// just wait for the first event
+				<-eventCh
+			}
+
+			p := Provider{}
+			p.SetDefaults()
+
+			p.AllowCrossNamespace = func(b bool) *bool { return &b }(test.allowCrossNamespace)
+			conf := p.loadConfigurationFromCRD(context.Background(), client)
+			assert.Equal(t, test.expected, conf)
+		})
+	}
+}

pkg/provider/kubernetes/crd/kubernetes_udp.go

@@ -36,7 +36,7 @@ func (p *Provider) loadIngressRouteUDPConfiguration(ctx context.Context, client
 			serviceName := makeID(ingressRouteUDP.Namespace, key)
 
 			for _, service := range route.Services {
-				balancerServerUDP, err := createLoadBalancerServerUDP(client, ingressRouteUDP.Namespace, service)
+				balancerServerUDP, err := p.createLoadBalancerServerUDP(client, ingressRouteUDP.Namespace, service)
 				if err != nil {
 					logger.
 						WithField("serviceName", service.Name).
@@ -77,9 +77,13 @@ func (p *Provider) loadIngressRouteUDPConfiguration(ctx context.Context, client
 	return conf
 }
 
-func createLoadBalancerServerUDP(client Client, namespace string, service v1alpha1.ServiceUDP) (*dynamic.UDPService, error) {
-	ns := namespace
+func (p *Provider) createLoadBalancerServerUDP(client Client, parentNamespace string, service v1alpha1.ServiceUDP) (*dynamic.UDPService, error) {
+	ns := parentNamespace
 	if len(service.Namespace) > 0 {
+		if !isNamespaceAllowed(p.AllowCrossNamespace, parentNamespace, service.Namespace) {
+			return nil, fmt.Errorf("udp service %s/%s is not in the parent resource namespace %s", service.Namespace, service.Name, ns)
+		}
+
 		ns = service.Namespace
 	}